Electrocardiogram at an altitude of 3600 m with reference to T wave depression

Introduction: Exposure to high altitude decreases arterial oxygen saturation (SaO₂ ). Previous studies have shown decreased voltage of the T wave of the electrocardiogram (ECG) at altitudes up to 7000 m (22,966 ft) secondary to hypoxia. This pilot study explored changes in the ECG at the maximum altitude pilots can fl y without supplemental oxygen. In addition, this is a common altitude for recreational trekkers. Methods: There were 13 subjects who rested at sea level (1ATA) for 30 min and then were taken to an altitude of 3000 m or 3600 m (10,000 or 12,000 ft; at altitude) where they rested for 30 min. ECG was collected continuously as was SaO₂ and heart rate (HR). A series of 10 ECG complexes were analyzed for 7 time periods over the 30-min collection periods. Results: The P wave, PR, QRS, and QT interval duration did not show a signifi cant difference between 1 ATA and at altitude for the group of subjects analyzed ( N=11). The T wave amplitude showed a signifi cant decrease ( δ=-19.3%) for seven subjects at altitude; however, the other six subjects did not show a signifi cant change ( δ=1.6%). The T wave amplitude observations described above were consistent for average HRs and selected HRs that were equal between 1 ATA and at altitude. Conclusion: This study confi rmed that some subjects showed decreased T wave amplitude at altitude which was not associated with pulmonary function, HR, ventilation, end-tidal CO₂ , or SaO₂ .